Dissolution principle: the core logic of chemical decomposition

Digestion is the process of using chemical reagents (such as strong acids, strong bases, or oxidants) to destroy organic and inorganic substances in a sample under heating conditions, converting them into soluble ions or gases, and providing clear solutions for subsequent analysis (such as ICP-MS, atomic absorption). Common methods include:

Acid digestion: Using strong acids such as nitric acid (HNO3) and hydrochloric acid (HCl), organic matter is decomposed through redox reactions. For example, nitric acid hydrochloric acid mixed acid (aqua regia) is commonly used for soil digestion to dissolve heavy metals.

Microwave digestion: using microwave heating to accelerate the reaction and shorten the digestion time (from several hours to several tens of minutes). For example, microwave digestion of biological samples (such as blood and tissue) in a closed container can avoid the loss of volatile elements (such as mercury).

High pressure digestion: By using a high-pressure tank to increase the reaction temperature (up to 200 ℃ or above), it is suitable for difficult to digest samples such as plastics and rubber. For example, polyethylene digestion requires heating with concentrated sulfuric acid in a high-pressure tank to 180 ℃.

Pipette operation: the key step for precise measurement

Choose a suitable pipette: Select the range according to the liquid volume (such as using a single channel pipette for 10-100 μ L and a multi-channel pipette for 1-10 mL), ensuring accuracy (error ≤ 0.5%).

Pre rinse suction head: Before suctioning the liquid, immerse the suction head in the solution three times, exhaust the air, and avoid diluting the sample with residual moisture.

Vertical suction: Insert the pipette vertically 1-2mm below the liquid level, slowly release the button to suction, and avoid inhaling bubbles.

Drainage technique: Hold the suction head tightly against the container wall, slowly press the button to the first gear (pre drainage), pause for 1 second, and then press to the second gear (drainage) to ensure there is no residue.

Novice precautions

Safety first: Wear protective goggles and gloves when dissolving, operate in a fume hood, and avoid inhaling acid mist or skin contact.

Avoid cross contamination: The pipette tip should be dedicated, and the digestion container (such as a PTFE tank) should be dedicated and labeled.

Record details: Record the type, dosage, temperature, and time of the digestion reagent for easy reproduction of experimental results.

Example: To analyze heavy metals in water samples, the sample can be first digested with a mixture of nitric acid and hydrogen peroxide using microwave digestion. Then, a 10mL pipette can be used to accurately remove the solution, which can be transferred to a volumetric flask for ICP-MS detection.